Jaundice (hyperbilirubinemia) in the newborn infant leads to kernicterus and frequently causes permanent damage to the central nervous system. This condition often results in severe and irreversible cerebral palsy or even death. Recently a phototherapy method has come to the fore as an extremely simple and quite effective means of reducing serum bilirubin levels to near normal. The merits of this treatment have been argued against possible damaging effects of irradiation and the lack of knowledge of the machanism of the photo-destruction of bilirubin in vivo and the absence of information on the structure and toxicity of the photo-products. Solutions to these problems are currently being sought by studying the in vitro photochemistry of bilirubin and model pyrrole and dipyrrole systems in our laboratory in terms of the machanism of breakdown, the structures of the products formed, and the toxicity of such products.